Problem: $ D = \left[\begin{array}{rrr}0 & 2 & 2 \\ 1 & 1 & 0 \\ 2 & 1 & 1\end{array}\right]$ What is $ D^{-1}$ ?
$ = \left[\begin{array}{rrr}-\frac{1}{4} & 0 & \frac{1}{2} \\ \frac{1}{4} & 1 & -\frac{1}{2} \\ \frac{1}{4} & -1 & \frac{1}{2}\end{array}\right]$